Recreational Vehicle and GFCI problems (long)

Discussion in 'General Electronics Chat' started by BillB3857, Jul 20, 2009.

  1. BillB3857

    Thread Starter Senior Member

    Feb 28, 2009
    2,400
    348
    I have a travel trailer with 30 amp service factory installed. Until this year, I have had no problems when using campground power connections. Twice this year, I have encountered power feeds that are GFCI protected at the campground source. Both times, the GFCI trips as soon as it is turned on if the trailer is connected. I opened all circuit breakers in my trailer, including the MAIN (which opens the hot lead feeding everything) and the GFCI still trips. I then disconnected (YES, I KNOW HOW UNSAFE THIS IS, BUT I'M TROUBLESHOOTING HERE) the ground wire at the plug end of my cord. No more trips. Since my trailer has metal jacks sitting on damp soil, if I had a high leakage within my trailer, it should have still tripped. I took my Fluke 77 meter and stuck one lead into the damp soil and touched the other lead to the trailer frame. I saw just a few millivolts of AC, much as seen with open leads near a source. After having power on the unit for a few hours with the ground wire disconnected at the plug, I put everything back to normal. NO MORE TRIPS??? Any ideas out there? I'v been reading the various RV forums and itd seems to be a fairly common problem but nobody seems to have a solid answer. By the way, I'm in the United States.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Sounds like perhaps your cord may have gotten wet, and the moisture wicked up inside the cable. There's enough moisture to cause current from the hot to the ground, which trips the GFCI.
     
  3. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    I'm no expert, but here are a few of my thoughts. And I've been very impressed with the expertise on this board, so if you folks find some errors in what I write, please correct me!

    First, a GFI circuit has really nothing to do with ground, despite the name. The basic principle of operation is as shown in the attached diagram. Please correct me if there are other designs out there that I'm not representing -- I'm trying to write a short document on common-sense AC safety and want to make sure everything is correct. Anyway, if the magnetic field sensing circuit detects any current (on the order of 2 mA or so), the relay contacts are open. This works regardless of whether there's a ground connection or not (for example, you could get an unbalanced current from e.g. an accidental connection to a 440 VAC line). I consider this a brilliant design (and straightforward application of Faraday's Law). Of course, there's nothing to protect you from a fatal shock should you touch the two power leads.

    Thus, if this is the correct principle of operation of the GFI, then the only thing that can cause a correctly-operating GFI to trip is an unbalanced current on the two power lines (hot and neutral), caused by current leakage to a conductor that isn't at the same potential as either of the two power leads.

    The big clue is that the problem went away when you disconnected the ground lead. I discount the jacks since you apparently didn't measure the resistance from the hookup ground the jack. You really don't know whether they were making adequate contact with ground.

    Thus, it seems to me you have an AC leakage problem somewhere in the trailer's circuitry. One of the first things I would suspect is the inverter, as I vaguely remember hearing someone complain that sometimes they're not as proper as they could be.

    I would also want to know why you still had leakage when the main circuit breaker was open. Is it possible the inverter is wired independently of the main circuit breaker (and, hopefully protected with its own fuse)? A leaky inverter would then explain what you saw. I just went out and checked my trailer and the inverter is powered through the main breaker.
     
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  4. BillB3857

    Thread Starter Senior Member

    Feb 28, 2009
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    Thanks for the responses. I tend to agree with Sgt. about the power cord. I found where it makes the initial splice after entering the trailer and disconnected the hot lead there. The GFI still tripped. Guess I will be looking for a replacement power cord. As for the inverter (DC to AC), I don't have one but I do have a CONVERTER (AC to 12VDC) and it is fed from a breaker after the Main breaker in the trailer. Sgt, could it be that after leaving the power applied to the cord with the ground disconnected that it dried itself out? The cord looks to be in good shape with no cuts in the outer jacket. It is almost 6 years old.
     
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